diff --git a/tools/rosmake/src/rosmake/engine.py b/tools/rosmake/src/rosmake/engine.py
index f2bf0bf6..acba0ccb 100755
--- a/tools/rosmake/src/rosmake/engine.py
+++ b/tools/rosmake/src/rosmake/engine.py
@@ -54,6 +54,9 @@ from . import package_stats
 
 from optparse import OptionParser
 
+# #3883
+_popen_lock = threading.Lock()
+
 def make_command():
     """
     @return: name of 'make' command
@@ -371,13 +374,19 @@ class RosMakeAll:
         if self.ros_parallel_jobs > 0:
             local_env['ROS_PARALLEL_JOBS'] = "-l%d" % self.ros_parallel_jobs
         elif "ROS_PARALLEL_JOBS" not in os.environ: #if no environment setup and no args fall back to # cpus
-            local_env['ROS_PARALLEL_JOBS'] = "-l%d" % parallel_build.num_cpus()
+            # num_cpus check can (on OS X) trigger a Popen(), which has
+            #the multithreading bug we wish to avoid on Py2.7.
+            with _popen_lock:
+                local_env['ROS_PARALLEL_JOBS'] = "-l%d" % parallel_build.num_cpus()
         local_env['SVN_CMDLINE'] = "svn --non-interactive"
         cmd = ["bash", "-c", "cd %s && %s "%(self.rospack.get_path(package), make_command()) ] #UNIXONLY
         if argument:
             cmd[-1] += argument
         self.printer.print_full_verbose (cmd)
-        command_line = subprocess.Popen(cmd, stdout=subprocess.PIPE,  stderr=subprocess.STDOUT, env=local_env, preexec_fn=self._subprocess_setup)
+        # #3883: make sure only one Popen command occurs at a time due to
+        # http://bugs.python.org/issue13817
+        with _popen_lock:
+            command_line = subprocess.Popen(cmd, stdout=subprocess.PIPE,  stderr=subprocess.STDOUT, env=local_env, preexec_fn=self._subprocess_setup)
         (pstd_out, pstd_err) = command_line.communicate() # pstd_err should be None due to pipe above
         return (command_line.returncode, pstd_out)